1. Field of the Invention
The present invention relates generally to a method and an appartus for recording a digital information signal and more particularly is directed to a method and an apparatus for recording a digital information signal on a recording medium by using a rotary magnetic head.
2. Description of the Prior Art
It is proposed in the art that when a video signal and an audio signal are recorded on a magnetic tape as one slant track at each unit time by using a rotary head assembly of helical scan type and then reproduced therefrom, the video signal and the audio signal are pulse-code-modulated (PCM) and then recorded and reproduced. The reason for this is that if the video signal and so on are pulse-code-modulated, recording and reproducing with high information accuracy becomes possible.
In this case, in a conventional video tape recorder (VTR), tracking control is provided so as to make the rotary head trace correctly the record track upon reproducing. That is, upon recording, tracking control is carried out using a control signal which is recorded along one edge of the magnetic tape in its width direction by a stationary or fixed magnetic head, so that when reproduced by the fixed head the reproduced control signal and the rotary phase of the rotary head have a constant phase relation therebetween.
In this method, however, a special fixed magnetic head must be provided for the tracking control. When the recording and reproducing apparatus is desired to be made small in size, such fixed magnetic head causes a disadvantage in view of the mounting place thereof and so on.
Therefore, as a tracking control method without using the fixed head, there is proposed the following method.
In this method, for example, an analog video signal is recorded and reproduced under a so-called successive state (under the state that a guard band is not formed between the adjacent tracks), in which a tracking pilot signal is recorded by the rotary head on the track on which the video signal is recorded. In this case, the pilot signal exists in the low frequency band side wherein the record signal of the video signal does not exist in view of the frequency spectrum so that upon reproducing, the pilot signal can be separated with ease.
This method, however, employs a signal with a relatively low frequency as the pilot signal so that it is rather difficult to erase the pilot signal. Therefore, when a signal, while erasing the signal which was previously recorded, is newly recorded on that portion, there occurs a disadvantage that the preceding recorded signal remains. Depending on the modulation system, when the information signal to be recorded has a spectrum in the low frequency band just like the PCM signal, it is quite difficult to separate the pilot signal. Furthermore, since the frequencies of four kinds are used as the pilot signal, the construction of the circuit becomes complicated.